Anode and method of continuous plating



E. J. NEWTON ANODE AND METHOD OF CONTINUOUS PLATING Jan. 8, 1957 2 Sheets-Sheet 1 Filed May 5, 1949 TIL I. QM V E m h. m 1 L Ntll m W \m- W W n H- I Nwm INVENTOR d. New/1'00 Elmo/e (@7 1957 E. J. NEWTON ANODE AND METHOD OF CONTINUOUS PLATING 2 Sheets-Sheet 2 Filed May 5, 1949 M n 4kg? W 5 m 2 6 W 1 1 mp 5 Z II II LI. a i :1 1 ow w Q .m m @H IIGIW 7 M MD 1 q d 0 :9 v M /B 6 1 m l P i||lk17 B 2,776,939 Patented Jan. 8, 1957 ANODE AND METHOD OF CONTINUOUS PLATING Application May 5, 1949, Serial No. 91,612 Claims. (Cl. 204-28) This invention relates to the continuous electrotinning of metal. It has especial applicability to the continuous alkaline electrotinning of ferrous metal and for purposes of explanation and illustration will be described in connection with the continuous, alkaline electrotinning of steel. In the continuous alkaline electrotinning of steel, steel generally in strip form, is passed continuously through an alkaline electrolytic tinning bath between anodes of tin which are immersed in the bath. The strip acts as the cathode, the tin passing from the anodes through the alkaline electrolyte and being deposited upon the surfaces of the strip. It is desirable that the tin coatmg deposited upon the strip be of substantially uniform thickness throughout the surface of the strip.

It has been found in using tin anodes of the solid slab type in the continuous tinning of strip that there is a differential in coating weight from the edges to the center of the strip, The coating is heavier at the edges than at the center on strip narrower than the anodes but lighter at the edges than at the center on strip wider than the anodes. This lack of uniformity is considerably more pronounced in the alkaline process than in the acid process because of the superior throwing power of the alkaline electrolyte. Attempts to overcome this edge to center differential and to obtain uniform distribution of the tin coating across the full width of the strip have been generally unsuccessful.

In the alkaline process it is necessary to deposit from a quadrivalent rather than a divalent tin solution to permit brightening the as-plated, satin finished, matte coat ing by melting and divalent solution will quenching. Tin deposited from a not brighten. The tin anodes are put into solution in the quadrivalent form by charging them with a high current density until a greenish-yellow or brownish film is formed on the submerged surfaces, and only then may the current density be lowered to normal operating values. So long as this film is retained, satisfactory plating and brightening may be obtained.

My invention provides an anode for continuous electrolytic tin plating in alkaline electrolyte comprising a supporting head and a plurality of electrode members parallel to each other and spaced apart to such an extent that a continuous anode film is formed on each anode surface during the plating operation. Such an electrode may be formed either as a slab electrode having a slot extending from the bottom edge to a point adjacent the top or it may be an adjustable electrode having a supporting head adapted to carry individual electrode members which may be adjustably spaced apart from one another. In any instance the slot must extend above the surface of the alkaline bath for the reason that a discontinuity in the anode film will appear at the terminus of the slot if it is submerged in the bath, resulting in the deposition of spongy, gray tin which will not brighten upon subsequent treatment.

In practice it has been found that a spacing between the electrode members substantially equal to their thicka defect which is commercially undesirable.

ness is most satisfactory for producing the desired reduction of edge to center coating difierential. However, the distance may be greater or less than the anode thickness, limited only to a distance such that current interference from the two electrode members will not cause a discontinuity in the anode film. I have found as a practical matter that the minimum distance between electrode members is about one-half their thickness.

In the method of my invention, slotted anodes are suspended in pairs in an alkaline electrotinning bath, either alone or in conjunction with pairs of conventional slabtype electrodes, and the strip is passed between the series of anodes so that the slotted anodes may correct the edge to center coating differential on strip narrower than the anodes, by increasing the amount of tin deposited on the center. The edges of the strip are not affected by this method. The electrode of my invention when used alone or in combination with conventional slab electrodes, has been found to reduce the objectionably high edge to center tin coating differential and to produce a more highly satisfactory commercial product. It is simple in construction and readily adapted to ordinary commercial tinning lines without major alterations.

In the accompanying drawings illustrating a present preferred embodiment of my invention:

Figure 1 is a schematic diagram of one form of a continuous electrotinning line;

Figure 2 is an elevation of a conventional slab anode as ordinarily used in the electrotinning line shown in Figure 1;

Figure 3 is a front elevation of a slotted slab electrode according to my invention;

Figure 4 is a side elevation of the same electrode;

Figure 5 is a front elevation of an adjustable electrode according to my invention; and

Figure 6 is a section on the line VI-VI of Figure 5.

Referring first to Figure 1, I have illustrated a tinning line comprising a tank 2 containing an alkaline electrolyte which may be a solution of sodium stannate and sodium hydroxide or the salt of some other base such as potassium. Slab anodes 3 of generally rectangular shape with shoulders 3a are suspended in the electrolyte on bars 4 (see Figure 2).

In the method of my invention pairs of slotted anodes are substituted for pairs of the solid slab type anode at any point in the tinning line. The line is equipped with upper guide rolls 5 and lower guide rolls 6. The steel strip 7 which is to be coated is passed alternately over these upper and lower guide rolls so that its surfaces lie substantially parallel to the sides of the anodes. The anodes rest on the bars 4, through which they are connected to a source of direct current electrical energy not shown in the drawings. The strip 7 is made the cathode of the electrolytic cell by being connected to a source of direct current energy not shown in the drawings.

In Figure 3 I have illustrated a slab electrode 8 having a supporting head 9 and a pair of downwardly extending electrode members 10. A slot 11 extending the full working length of the electrode separates the electrode members 10 by a distance substantially equal to their thickness.

Another embodiment of my invention, illustrated in Figure 5 has a supporting head 12 with a copper buss bar 13 mounted on its upper edge to act as a bearing and conducting member. A pair of hangers 14- are slidably mounted in a vertical longitudinal slot 15 extending cenr trally of the supporting head 12 and the buss bar 13.

An electrode member 16 is cast about one end of each of the hangers 14 so as to be suspended therefrom when a hanger is in position in the slot 15. Bearing members 17, adapted to rest upon and slide longitudinally of the buss bar 13, are removably attached to the ends of the hangers 14 opposite the electrode members 16 by bolts 18' or other suitable means. The bearing members act to support the hangers and electrode members on the supporting head 12 and to make contact between the buss bar 13 and the electrode members 16.

Each bearing member 17' has a projecting portion 19 with a threaded opening 20 adapted to take an adjusting.

screw 21. The adjusting screw 21' is divided into two portions 22and23. 'Ihe threaded openings 20 of the projecting portions 19 are threaded in opposite directions so as to engage the two threaded portions 22 and 23 of the adjusting screw. The adjusting screw has an end portion 24 adapted to cooperate with a turning means and is rotatably journaled adjacent the end portion 24 in a projecting flange 25 on the supporting head. Rotation of the adjusting screw causes the bearing members 17 to move in opposite directions relative to the supporting head 12' thereby adjusting the distance between the electrode members 16.

As the slotted anodes are used, their thickness decreases and the slot width increases. This materially reduces the ability of the anode to deposit a heavier coating in the center of the strip. To maintain the efficiency of the slot, an adjustable anode, illustrated in Figures and 6-may be used to maintain a constant slot Width anode thickness ratio.

Furthermore, I have found it to be advantageous, when using the adjustable anode of my invention in a continuous plating line in conjunction with conventional slab anodes, to increase the slot widthtuntilthe outside edges of the electrodes are parallel to the edges of strip wider than the slab anodes. This acts to increase the deposition of tin on the edges and eliminate the edge center coating differential on strip wider than the conventional anodes.

By using the electrode of my invention in a continuous tin-plating line it is possible to maintain a minimum edge to center coating differential in the tin coating on the strip. This result is derived from the more uniform distribution of current about the electrode which is achieved by my invention. The solid-head slotted anode will correct coatings on stri narrower than the slab anodes used in conjunction with it. The adjustable-head anode may beused to correct coatings on all widths of strip.

While I have illustrated and described a present preferred embodimentof my invention and method of using the'same it will be understood that it may be otherwise embodied within the scope of the following claims.

I claim:

1. In a continuous alkaline electrotinning line having means for continuously passing a metal strip to be plated through an alkaline electrotinning bath, an anode comprisinga supporting head, a vertical longitudinal slot in said head, a pair of electrode members movably mounted in said slot and extending outwardly from the supporting head side-by-side in the same general plane substantially across thewidth of the strip and having the portion of each member connected to the supporting head extending above the surface of the electrotinning bath at all times and adjustingmeans for moving the electrode members relatively to each other.

2. In a continuous alkaline electrotinning line having means'for continuously passing a metal strip to be plated through an alkaline electrotinning line, an anode comprising a supporting head, a vertical longitudinal slot in said head, a pair of electrode members slidably mounted in said slot and in electrical contact with the head, said members extending substantially across the width of the strip and having the portion of each member connected with the supporting head extending above the surface of the electrotinning bath at all times and screw means cooperating with the head and with the electrode members to move the-electrode membersrelatively to each other.

3. In a continuous alkaline electrotinning line having means for continuously passing a metal strip to be plated, an anode comprising a supporting head, a metallic conductor forming a part of said head, a vertical longitudinal slot centrally of said head, a pair of hanger members slidably mounted in said slot and adapted to rest upon and be in electrical contact with the metallic conductor, an electrode member fixedly mounted to each member and extending outward therefrom, said electrode members extending substantially across the width of the strip and having the portion of each member connected to the hanger members extending above the surface of the electrotinning bath at all times, and screw means cooperating with the head and with the electrode members to move the electrode members relatively to each other.

4. In a continuous alkaline bath electrotinning line for the plating of metal strips where a tendency of the plating is to form a differential thickness between the plating at the edges and the plating at the, center of the strip, the method of regulating the plating thickness which comprises the steps of passing the strip between the anodes of successive series of pairs of anodes, at least some of which pairs are provided with a supporting head and a pair of. adjustable electrode members extending from the head into the alkaline bath, maintaining said members substantially parallel to each other and spaced apart from. each other in the bathto such an extent that a continuously. anode film is formed about the surface of each anode member during the tinning operation, and maintaining thesoutside edges of the electrode members substantially parallel= to the outside edge of the strip being plated while at the same time maintaining the end of'the electrode members attached to the supporting head above the surface of'the electrotinning bath.

5; In a continuous alkaline bath electrotinning line'for theplating of metalstrips-where a tendency of the plating is to form a differential thickness between the plating at the edges and' theplating at the center of the strip, a method of controlling the plating differential which comprises passing the strip between the anodes of successsive series of paired anodes at least some of which pairs are provided with a'supportinghead and a pair of adjacent electrode members extending from the head through the alkaline bath maintaining said members substantially parallel toeach other and spaced apart from each other in the bath by a distance substantially equal to their thickness and maintaining the outside edges of the electrode members substantially parallel to the outside edge of the strip being plated while at the same time maintaining the end of the electrode member attached to the supporting head above the surface of the electrotinning bath.

References Citedinthe file of this patent UNITED STATES PATENTS 733,602 Starrett July 14, 1903 1,154,092. Burdctte Sept. 21, 1915 2,043,698 Dyer June 9, 1936 2,312,452 Taylerson Mar. 2, 1943 2,317,242 Allen et al. Apr, 20, 1943 2,341,158 Nachtman Feb. 8, 1944 2,382,018 Martin Aug. 14, 1945 2,450,509 Glock Oct. 5, 1948 2,462,506 Klein Feb. 22, 1949 2,544,510 Prahl Mar. 6, 1951 2,554,943 Farmer May 29, 1951 FOREIGN PATENTS 14,823 Great Britain of 1903 OTHER REFERENCES The Metal Industry, June 26, 1942, pages 435-438. Transactions of the Electrochemical Society, vol. 84 (19431). Pages 249 to 254. An article by Glock. 

1. IN A CONTINUOUS ALKALINE ELECTROTINNING LINE HAVING MEANS FOR CONTINUOUSLY PASSING A METAL STRIP TO BE PLATED THROUGH AN ALKALINE ELECTROTINNING BATH, AN ANODE COMPRISING A SUPPORTING HEAD, A VERTICAL LONGITUDINAL SLOT IN SAID HEAD, A PAIR OF ELECTRODE MEMBERS MOVABLY MOUNTED IN SAID SLOT AND EXTENDING OUTWARDLY FROM THE SUPPORTING HEAD SIDE-BY-SIDE IN THE SAME GENERAL PLANE SUBSTANTIALLY ACROSS THE WIDTH OF THE STRIP AND HAVING THE PORTION OF EACH MEMBER CONNECTED TO THE SUPPORTING HEAD EXTENDING ABOVE THE SURFACE OF THE ELECTROTINNING BATH AT ALL TIMES AND ADJUSTING MEANS FOR MOVING THE ELECTRODE MEMBERS RELATIVELY TO EACH OTHER. 